blob: b5156d631681bbae75175eac8f137b253e891507 [file] [log] [blame]
bellardacd935e2004-11-15 22:57:26 +00001@example
2@c man begin SYNOPSIS
Denis V. Lunev10985132016-06-17 17:44:13 +03003@command{qemu-img} [@var{standard} @var{options}] @var{command} [@var{command} @var{options}]
bellardacd935e2004-11-15 22:57:26 +00004@c man end
5@end example
6
Kevin Wolf48467322012-08-16 10:56:35 +02007@c man begin DESCRIPTION
8qemu-img allows you to create, convert and modify images offline. It can handle
9all image formats supported by QEMU.
10
11@b{Warning:} Never use qemu-img to modify images in use by a running virtual
12machine or any other process; this may destroy the image. Also, be aware that
13querying an image that is being modified by another process may encounter
14inconsistent state.
15@c man end
16
bellardacd935e2004-11-15 22:57:26 +000017@c man begin OPTIONS
18
Denis V. Lunev10985132016-06-17 17:44:13 +030019Standard options:
20@table @option
21@item -h, --help
22Display this help and exit
23@item -V, --version
24Display version information and exit
Denis V. Lunev06a1e0c2016-06-17 17:44:14 +030025@item -T, --trace [[enable=]@var{pattern}][,events=@var{file}][,file=@var{file}]
26@findex --trace
27@include qemu-option-trace.texi
Denis V. Lunev10985132016-06-17 17:44:13 +030028@end table
29
bellardacd935e2004-11-15 22:57:26 +000030The following commands are supported:
Stuart Brady153859b2009-06-07 00:42:17 +010031
32@include qemu-img-cmds.texi
bellardacd935e2004-11-15 22:57:26 +000033
34Command parameters:
35@table @var
Fam Zhengc150eb92018-02-09 13:29:13 +080036
bellardacd935e2004-11-15 22:57:26 +000037@item filename
Fam Zhengc150eb92018-02-09 13:29:13 +080038is a disk image filename
Daniel P. Berrangeeb769f72016-02-17 10:10:20 +000039
ths5fafdf22007-09-16 21:08:06 +000040@item fmt
Kevin Wolff932c042009-10-28 12:49:15 +010041is the disk image format. It is guessed automatically in most cases. See below
42for a description of the supported disk formats.
bellardacd935e2004-11-15 22:57:26 +000043
ths5fafdf22007-09-16 21:08:06 +000044@item size
Kevin Wolfeff44262009-06-04 15:39:39 +020045is the disk image size in bytes. Optional suffixes @code{k} or @code{K}
46(kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M)
47and T (terabyte, 1024G) are supported. @code{b} is ignored.
bellardacd935e2004-11-15 22:57:26 +000048
49@item output_filename
ths5fafdf22007-09-16 21:08:06 +000050is the destination disk image filename
bellardacd935e2004-11-15 22:57:26 +000051
52@item output_fmt
Fam Zhengc150eb92018-02-09 13:29:13 +080053is the destination format
54
Kevin Wolfeff44262009-06-04 15:39:39 +020055@item options
56is a comma separated list of format specific options in a
57name=value format. Use @code{-o ?} for an overview of the options supported
Kevin Wolf3e032362009-10-28 12:49:17 +010058by the used format or see the format descriptions below for details.
Fam Zhengc150eb92018-02-09 13:29:13 +080059
Wenchao Xiaef806542013-12-04 17:10:57 +080060@item snapshot_param
61is param used for internal snapshot, format is
62'snapshot.id=[ID],snapshot.name=[NAME]' or '[ID_OR_NAME]'
Fam Zhengc150eb92018-02-09 13:29:13 +080063
Fam Zhengc150eb92018-02-09 13:29:13 +080064@end table
65
66@table @option
67
68@item --object @var{objectdef}
69is a QEMU user creatable object definition. See the @code{qemu(1)} manual
70page for a description of the object properties. The most common object
71type is a @code{secret}, which is used to supply passwords and/or encryption
72keys.
73
74@item --image-opts
75Indicates that the source @var{filename} parameter is to be interpreted as a
76full option string, not a plain filename. This parameter is mutually
77exclusive with the @var{-f} parameter.
78
79@item --target-image-opts
80Indicates that the @var{output_filename} parameter(s) are to be interpreted as
81a full option string, not a plain filename. This parameter is mutually
82exclusive with the @var{-O} parameters. It is currently required to also use
83the @var{-n} parameter to skip image creation. This restriction may be relaxed
84in a future release.
85
Fam Zhenga7e326d2018-02-09 13:29:14 +080086@item --force-share (-U)
87If specified, @code{qemu-img} will open the image in shared mode, allowing
88other QEMU processes to open it in write mode. For example, this can be used to
89get the image information (with 'info' subcommand) when the image is used by a
90running guest. Note that this could produce inconsistent results because of
91concurrent metadata changes, etc. This option is only allowed when opening
92images in read-only mode.
93
Fam Zhengc150eb92018-02-09 13:29:13 +080094@item --backing-chain
95will enumerate information about backing files in a disk image chain. Refer
96below for further description.
97
bellardacd935e2004-11-15 22:57:26 +000098@item -c
Fam Zhengb8550432018-07-27 11:34:00 +080099indicates that target image must be compressed (qcow format only)
Fam Zhengc150eb92018-02-09 13:29:13 +0800100
blueswir1d2c639d2009-01-24 18:19:25 +0000101@item -h
102with or without a command shows help and lists the supported formats
Fam Zhengc150eb92018-02-09 13:29:13 +0800103
Jes Sorensenaaf55b42011-07-19 15:01:34 +0200104@item -p
Kevin Wolf0e3bd992014-01-20 15:12:16 +0100105display progress bar (compare, convert and rebase commands only).
106If the @var{-p} option is not used for a command that supports it, the
Max Reitz262fbae2017-02-08 00:57:57 +0100107progress is reported when the process receives a @code{SIGUSR1} or
108@code{SIGINFO} signal.
Fam Zhengc150eb92018-02-09 13:29:13 +0800109
Miroslav Rezaninaf382d432013-02-13 09:09:40 +0100110@item -q
111Quiet mode - do not print any output (except errors). There's no progress bar
112in case both @var{-q} and @var{-p} options are used.
Fam Zhengc150eb92018-02-09 13:29:13 +0800113
Kevin Wolfa22f1232011-08-26 15:27:13 +0200114@item -S @var{size}
115indicates the consecutive number of bytes that must contain only zeros
116for qemu-img to create a sparse image during conversion. This value is rounded
117down to the nearest 512 bytes. You may use the common size suffixes like
Fam Zhengb8550432018-07-27 11:34:00 +0800118@code{k} for kilobytes.
Fam Zhengc150eb92018-02-09 13:29:13 +0800119
Kevin Wolf3763f262011-12-07 13:57:13 +0100120@item -t @var{cache}
121specifies the cache mode that should be used with the (destination) file. See
122the documentation of the emulator's @code{-drive cache=...} option for allowed
123values.
Fam Zhengc150eb92018-02-09 13:29:13 +0800124
Max Reitz40055952014-07-22 22:58:42 +0200125@item -T @var{src_cache}
Stefan Hajnoczibb87fdf2014-09-02 11:01:02 +0100126specifies the cache mode that should be used with the source file(s). See
127the documentation of the emulator's @code{-drive cache=...} option for allowed
128values.
Fam Zhengc150eb92018-02-09 13:29:13 +0800129
blueswir1d2c639d2009-01-24 18:19:25 +0000130@end table
131
132Parameters to snapshot subcommand:
133
134@table @option
135
136@item snapshot
137is the name of the snapshot to create, apply or delete
138@item -a
139applies a snapshot (revert disk to saved state)
140@item -c
141creates a snapshot
142@item -d
143deletes a snapshot
144@item -l
145lists all snapshots in the given image
bellardacd935e2004-11-15 22:57:26 +0000146@end table
147
Miroslav Rezaninad14ed182013-02-13 09:09:41 +0100148Parameters to compare subcommand:
149
150@table @option
151
152@item -f
153First image format
154@item -F
155Second image format
156@item -s
Daniel P. Berrangeb6af0972015-08-26 12:17:13 +0100157Strict mode - fail on different image size or sector allocation
Miroslav Rezaninad14ed182013-02-13 09:09:41 +0100158@end table
159
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100160Parameters to convert subcommand:
161
162@table @option
163
164@item -n
165Skip the creation of the target volume
Peter Lieven2d9187b2017-02-28 13:40:07 +0100166@item -m
167Number of parallel coroutines for the convert process
168@item -W
169Allow out-of-order writes to the destination. This option improves performance,
170but is only recommended for preallocated devices like host devices or other
171raw block devices.
Fam Zhenge11ce122018-07-27 11:34:01 +0800172@item -C
173Try to use copy offloading to move data from source image to target. This may
174improve performance if the data is remote, such as with NFS or iSCSI backends,
175but will not automatically sparsify zero sectors, and may result in a fully
176allocated target image depending on the host support for getting allocation
177information.
Max Reitz8eaac022019-05-07 22:35:03 +0200178@item --salvage
179Try to ignore I/O errors when reading. Unless in quiet mode (@code{-q}), errors
180will still be printed. Areas that cannot be read from the source will be
181treated as containing only zeroes.
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100182@end table
183
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200184Parameters to dd subcommand:
185
186@table @option
187
188@item bs=@var{block_size}
189defines the block size
190@item count=@var{blocks}
191sets the number of input blocks to copy
192@item if=@var{input}
193sets the input file
194@item of=@var{output}
195sets the output file
Reda Sallahif7c15532016-08-10 16:16:09 +0200196@item skip=@var{blocks}
197sets the number of input blocks to skip
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200198@end table
199
bellardacd935e2004-11-15 22:57:26 +0000200Command description:
201
202@table @option
John Snow83e6da02018-05-03 18:56:45 -0400203
John Snow13c24ed2019-04-09 17:06:55 -0400204@item amend [--object @var{objectdef}] [--image-opts] [-p] [-q] [-f @var{fmt}] [-t @var{cache}] -o @var{options} @var{filename}
John Snow83e6da02018-05-03 18:56:45 -0400205
206Amends the image format specific @var{options} for the image file
207@var{filename}. Not all file formats support this operation.
208
John Snow9775fcd2018-05-03 18:56:47 -0400209@item bench [-c @var{count}] [-d @var{depth}] [-f @var{fmt}] [--flush-interval=@var{flush_interval}] [-n] [--no-drain] [-o @var{offset}] [--pattern=@var{pattern}] [-q] [-s @var{buffer_size}] [-S @var{step_size}] [-t @var{cache}] [-w] [-U] @var{filename}
Kevin Wolfb6133b82014-08-05 14:17:13 +0200210
Kevin Wolfb6495fa2015-07-10 18:09:18 +0200211Run a simple sequential I/O benchmark on the specified image. If @code{-w} is
212specified, a write test is performed, otherwise a read test is performed.
213
214A total number of @var{count} I/O requests is performed, each @var{buffer_size}
Kevin Wolfd3199a32015-07-10 18:09:18 +0200215bytes in size, and with @var{depth} requests in parallel. The first request
Kevin Wolf83de9be2015-07-13 13:13:17 +0200216starts at the position given by @var{offset}, each following request increases
217the current position by @var{step_size}. If @var{step_size} is not given,
218@var{buffer_size} is used for its value.
Kevin Wolfb6133b82014-08-05 14:17:13 +0200219
Kevin Wolf55d539c2016-06-03 13:59:41 +0200220If @var{flush_interval} is specified for a write test, the request queue is
221drained and a flush is issued before new writes are made whenever the number of
222remaining requests is a multiple of @var{flush_interval}. If additionally
223@code{--no-drain} is specified, a flush is issued without draining the request
224queue first.
225
Kevin Wolfb6133b82014-08-05 14:17:13 +0200226If @code{-n} is specified, the native AIO backend is used if possible. On
227Linux, this option only works if @code{-t none} or @code{-t directsync} is
228specified as well.
229
Kevin Wolfb6495fa2015-07-10 18:09:18 +0200230For write tests, by default a buffer filled with zeros is written. This can be
231overridden with a pattern byte specified by @var{pattern}.
232
John Snow9775fcd2018-05-03 18:56:47 -0400233@item check [--object @var{objectdef}] [--image-opts] [-q] [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] [-U] @var{filename}
Kevin Wolfe6184692011-01-17 15:35:28 +0100234
Federico Simoncelli8599ea42013-01-28 06:59:47 -0500235Perform a consistency check on the disk image @var{filename}. The command can
236output in the format @var{ofmt} which is either @code{human} or @code{json}.
Max Reitz987402c2019-05-15 09:59:16 +0200237The JSON output is an object of QAPI type @code{ImageCheck}.
Kevin Wolfe6184692011-01-17 15:35:28 +0100238
Kevin Wolf4534ff52012-05-11 16:07:02 +0200239If @code{-r} is specified, qemu-img tries to repair any inconsistencies found
240during the check. @code{-r leaks} repairs only cluster leaks, whereas
241@code{-r all} fixes all kinds of errors, with a higher risk of choosing the
Stefan Weil0546b8c2012-08-10 22:03:25 +0200242wrong fix or hiding corruption that has already occurred.
Kevin Wolf4534ff52012-05-11 16:07:02 +0200243
Kevin Wolfe6184692011-01-17 15:35:28 +0100244Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
245consistency checks.
246
Max Reitzd6635c42014-06-02 22:15:21 +0200247In case the image does not have any inconsistencies, check exits with @code{0}.
248Other exit codes indicate the kind of inconsistency found or if another error
249occurred. The following table summarizes all exit codes of the check subcommand:
250
251@table @option
252
253@item 0
254Check completed, the image is (now) consistent
255@item 1
256Check not completed because of internal errors
257@item 2
258Check completed, image is corrupted
259@item 3
260Check completed, image has leaked clusters, but is not corrupted
261@item 63
262Checks are not supported by the image format
263
264@end table
265
266If @code{-r} is specified, exit codes representing the image state refer to the
267state after (the attempt at) repairing it. That is, a successful @code{-r all}
268will yield the exit code 0, independently of the image state before.
269
John Snow9775fcd2018-05-03 18:56:47 -0400270@item commit [--object @var{objectdef}] [--image-opts] [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename}
bellardacd935e2004-11-15 22:57:26 +0000271
Jeff Cody37222902014-01-24 09:02:37 -0500272Commit the changes recorded in @var{filename} in its base image or backing file.
273If the backing file is smaller than the snapshot, then the backing file will be
274resized to be the same size as the snapshot. If the snapshot is smaller than
275the backing file, the backing file will not be truncated. If you want the
276backing file to match the size of the smaller snapshot, you can safely truncate
277it yourself once the commit operation successfully completes.
bellardacd935e2004-11-15 22:57:26 +0000278
Max Reitz9a86fe42014-10-24 15:57:38 +0200279The image @var{filename} is emptied after the operation has succeeded. If you do
280not need @var{filename} afterwards and intend to drop it, you may skip emptying
281@var{filename} by specifying the @code{-d} flag.
282
Max Reitz1b22bff2014-10-24 15:57:40 +0200283If the backing chain of the given image file @var{filename} has more than one
284layer, the backing file into which the changes will be committed may be
285specified as @var{base} (which has to be part of @var{filename}'s backing
286chain). If @var{base} is not specified, the immediate backing file of the top
Max Reitz67e56472017-10-26 09:59:47 +0200287image (which is @var{filename}) will be used. Note that after a commit operation
288all images between @var{base} and the top image will be invalid and may return
289garbage data when read. For this reason, @code{-b} implies @code{-d} (so that
290the top image stays valid).
Max Reitz1b22bff2014-10-24 15:57:40 +0200291
John Snow9775fcd2018-05-03 18:56:47 -0400292@item compare [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-q] [-s] [-U] @var{filename1} @var{filename2}
Miroslav Rezaninad14ed182013-02-13 09:09:41 +0100293
294Check if two images have the same content. You can compare images with
295different format or settings.
296
297The format is probed unless you specify it by @var{-f} (used for
298@var{filename1}) and/or @var{-F} (used for @var{filename2}) option.
299
300By default, images with different size are considered identical if the larger
301image contains only unallocated and/or zeroed sectors in the area after the end
302of the other image. In addition, if any sector is not allocated in one image
303and contains only zero bytes in the second one, it is evaluated as equal. You
304can use Strict mode by specifying the @var{-s} option. When compare runs in
305Strict mode, it fails in case image size differs or a sector is allocated in
306one image and is not allocated in the second one.
307
308By default, compare prints out a result message. This message displays
309information that both images are same or the position of the first different
310byte. In addition, result message can report different image size in case
311Strict mode is used.
312
313Compare exits with @code{0} in case the images are equal and with @code{1}
314in case the images differ. Other exit codes mean an error occurred during
315execution and standard error output should contain an error message.
316The following table sumarizes all exit codes of the compare subcommand:
317
318@table @option
319
320@item 0
321Images are identical
322@item 1
323Images differ
324@item 2
325Error on opening an image
326@item 3
327Error on checking a sector allocation
328@item 4
329Error on reading data
330
331@end table
332
Fam Zhenge11ce122018-07-27 11:34:01 +0800333@item convert [--object @var{objectdef}] [--image-opts] [--target-image-opts] [-U] [-C] [-c] [-p] [-q] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-B @var{backing_file}] [-o @var{options}] [-l @var{snapshot_param}] [-S @var{sparse_size}] [-m @var{num_coroutines}] [-W] @var{filename} [@var{filename2} [...]] @var{output_filename}
bellardacd935e2004-11-15 22:57:26 +0000334
Thomas Huth46e8d272018-06-06 14:35:51 +0200335Convert the disk image @var{filename} or a snapshot @var{snapshot_param}
Wenchao Xiaef806542013-12-04 17:10:57 +0800336to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}
Kevin Wolfeff44262009-06-04 15:39:39 +0200337option) or use any format specific options like encryption (@code{-o} option).
bellardacd935e2004-11-15 22:57:26 +0000338
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100339Only the formats @code{qcow} and @code{qcow2} support compression. The
bellardacd935e2004-11-15 22:57:26 +0000340compression is read-only. It means that if a compressed sector is
341rewritten, then it is rewritten as uncompressed data.
342
bellardacd935e2004-11-15 22:57:26 +0000343Image conversion is also useful to get smaller image when using a
Stefan Hajnoczi550830f2014-09-16 15:24:24 +0100344growable format such as @code{qcow}: the empty sectors are detected and
345suppressed from the destination image.
bellardacd935e2004-11-15 22:57:26 +0000346
Peter Lieven11b66992013-10-24 12:07:05 +0200347@var{sparse_size} indicates the consecutive number of bytes (defaults to 4k)
348that must contain only zeros for qemu-img to create a sparse image during
349conversion. If @var{sparse_size} is 0, the source will not be scanned for
350unallocated or zero sectors, and the destination image will always be
351fully allocated.
352
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100353You can use the @var{backing_file} option to force the output image to be
354created as a copy on write image of the specified base image; the
355@var{backing_file} should have the same content as the input's base image,
356however the path, image format, etc may differ.
357
Fam Zhenga16efd52017-08-04 22:36:58 +0800358If a relative path name is given, the backing file is looked up relative to
359the directory containing @var{output_filename}.
360
Alexandre Derumierb2e10492013-09-02 19:07:24 +0100361If the @code{-n} option is specified, the target volume creation will be
362skipped. This is useful for formats such as @code{rbd} if the target
363volume has already been created with site specific options that cannot
364be supplied through qemu-img.
365
Peter Lieven2d9187b2017-02-28 13:40:07 +0100366Out of order writes can be enabled with @code{-W} to improve performance.
367This is only recommended for preallocated devices like host devices or other
368raw block devices. Out of order write does not work in combination with
369creating compressed images.
370
371@var{num_coroutines} specifies how many coroutines work in parallel during
372the convert process (defaults to 8).
373
John Snow9775fcd2018-05-03 18:56:47 -0400374@item create [--object @var{objectdef}] [-q] [-f @var{fmt}] [-b @var{backing_file}] [-F @var{backing_fmt}] [-u] [-o @var{options}] @var{filename} [@var{size}]
John Snow83e6da02018-05-03 18:56:45 -0400375
376Create the new disk image @var{filename} of size @var{size} and format
377@var{fmt}. Depending on the file format, you can add one or more @var{options}
378that enable additional features of this format.
379
380If the option @var{backing_file} is specified, then the image will record
381only the differences from @var{backing_file}. No size needs to be specified in
382this case. @var{backing_file} will never be modified unless you use the
383@code{commit} monitor command (or qemu-img commit).
384
385If a relative path name is given, the backing file is looked up relative to
386the directory containing @var{filename}.
387
388Note that a given backing file will be opened to check that it is valid. Use
389the @code{-u} option to enable unsafe backing file mode, which means that the
390image will be created even if the associated backing file cannot be opened. A
391matching backing file must be created or additional options be used to make the
392backing file specification valid when you want to use an image created this
393way.
394
395The size can also be specified using the @var{size} option with @code{-o},
396it doesn't need to be specified separately in this case.
397
John Snow9775fcd2018-05-03 18:56:47 -0400398@item dd [--image-opts] [-U] [-f @var{fmt}] [-O @var{output_fmt}] [bs=@var{block_size}] [count=@var{blocks}] [skip=@var{blocks}] if=@var{input} of=@var{output}
Reda Sallahi86ce1f62016-08-10 04:43:12 +0200399
400Dd copies from @var{input} file to @var{output} file converting it from
401@var{fmt} format to @var{output_fmt} format.
402
403The data is by default read and written using blocks of 512 bytes but can be
404modified by specifying @var{block_size}. If count=@var{blocks} is specified
405dd will stop reading input after reading @var{blocks} input blocks.
406
407The size syntax is similar to dd(1)'s size syntax.
408
John Snow9775fcd2018-05-03 18:56:47 -0400409@item info [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] [-U] @var{filename}
bellardacd935e2004-11-15 22:57:26 +0000410
411Give information about the disk image @var{filename}. Use it in
412particular to know the size reserved on disk which can be different
bellard19d36792006-08-07 21:34:34 +0000413from the displayed size. If VM snapshots are stored in the disk image,
Max Reitz987402c2019-05-15 09:59:16 +0200414they are displayed too.
blueswir1d2c639d2009-01-24 18:19:25 +0000415
Kashyap Chamarthye5357562012-10-18 11:25:34 +0530416If a disk image has a backing file chain, information about each disk image in
417the chain can be recursively enumerated by using the option @code{--backing-chain}.
418
419For instance, if you have an image chain like:
420
421@example
422base.qcow2 <- snap1.qcow2 <- snap2.qcow2
423@end example
424
425To enumerate information about each disk image in the above chain, starting from top to base, do:
426
427@example
428qemu-img info --backing-chain snap2.qcow2
429@end example
430
Max Reitz987402c2019-05-15 09:59:16 +0200431The command can output in the format @var{ofmt} which is either @code{human} or
432@code{json}. The JSON output is an object of QAPI type @code{ImageInfo}; with
433@code{--backing-chain}, it is an array of @code{ImageInfo} objects.
434
Max Reitz4db43902019-05-15 09:59:17 +0200435@code{--output=human} reports the following information (for every image in the
436chain):
437@table @var
438@item image
439The image file name
440
441@item file format
442The image format
443
444@item virtual size
445The size of the guest disk
446
447@item disk size
448How much space the image file occupies on the host file system (may be shown as
4490 if this information is unavailable, e.g. because there is no file system)
450
451@item cluster_size
452Cluster size of the image format, if applicable
453
454@item encrypted
455Whether the image is encrypted (only present if so)
456
457@item cleanly shut down
458This is shown as @code{no} if the image is dirty and will have to be
459auto-repaired the next time it is opened in qemu.
460
461@item backing file
462The backing file name, if present
463
464@item backing file format
465The format of the backing file, if the image enforces it
466
467@item Snapshot list
468A list of all internal snapshots
469
470@item Format specific information
471Further information whose structure depends on the image format. This section
472is a textual representation of the respective @code{ImageInfoSpecific*} QAPI
473object (e.g. @code{ImageInfoSpecificQCow2} for qcow2 images).
474@end table
475
John Snow13c24ed2019-04-09 17:06:55 -0400476@item map [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [-U] @var{filename}
Paolo Bonzinifacd6e22013-09-04 19:00:34 +0200477
478Dump the metadata of image @var{filename} and its backing file chain.
479In particular, this commands dumps the allocation state of every sector
480of @var{filename}, together with the topmost file that allocates it in
481the backing file chain.
482
483Two option formats are possible. The default format (@code{human})
484only dumps known-nonzero areas of the file. Known-zero parts of the
485file are omitted altogether, and likewise for parts that are not allocated
486throughout the chain. @command{qemu-img} output will identify a file
487from where the data can be read, and the offset in the file. Each line
488will include four fields, the first three of which are hexadecimal
489numbers. For example the first line of:
490@example
491Offset Length Mapped to File
4920 0x20000 0x50000 /tmp/overlay.qcow2
4930x100000 0x10000 0x95380000 /tmp/backing.qcow2
494@end example
495@noindent
496means that 0x20000 (131072) bytes starting at offset 0 in the image are
497available in /tmp/overlay.qcow2 (opened in @code{raw} format) starting
498at offset 0x50000 (327680). Data that is compressed, encrypted, or
499otherwise not available in raw format will cause an error if @code{human}
500format is in use. Note that file names can include newlines, thus it is
501not safe to parse this output format in scripts.
502
503The alternative format @code{json} will return an array of dictionaries
504in JSON format. It will include similar information in
505the @code{start}, @code{length}, @code{offset} fields;
506it will also include other more specific information:
507@itemize @minus
508@item
509whether the sectors contain actual data or not (boolean field @code{data};
510if false, the sectors are either unallocated or stored as optimized
511all-zero clusters);
512
513@item
514whether the data is known to read as zero (boolean field @code{zero});
515
516@item
517in order to make the output shorter, the target file is expressed as
518a @code{depth}; for example, a depth of 2 refers to the backing file
519of the backing file of @var{filename}.
520@end itemize
521
522In JSON format, the @code{offset} field is optional; it is absent in
523cases where @code{human} format would omit the entry or exit with an error.
524If @code{data} is false and the @code{offset} field is present, the
525corresponding sectors in the file are not yet in use, but they are
526preallocated.
527
528For more information, consult @file{include/block/block.h} in QEMU's
529source code.
530
Stefan Hajnoczifd03c2b2017-07-05 13:57:36 +0100531@item measure [--output=@var{ofmt}] [-O @var{output_fmt}] [-o @var{options}] [--size @var{N} | [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [-l @var{snapshot_param}] @var{filename}]
532
533Calculate the file size required for a new image. This information can be used
534to size logical volumes or SAN LUNs appropriately for the image that will be
535placed in them. The values reported are guaranteed to be large enough to fit
536the image. The command can output in the format @var{ofmt} which is either
Max Reitz987402c2019-05-15 09:59:16 +0200537@code{human} or @code{json}. The JSON output is an object of QAPI type
538@code{BlockMeasureInfo}.
Stefan Hajnoczifd03c2b2017-07-05 13:57:36 +0100539
540If the size @var{N} is given then act as if creating a new empty image file
541using @command{qemu-img create}. If @var{filename} is given then act as if
542converting an existing image file using @command{qemu-img convert}. The format
543of the new file is given by @var{output_fmt} while the format of an existing
544file is given by @var{fmt}.
545
546A snapshot in an existing image can be specified using @var{snapshot_param}.
547
548The following fields are reported:
549@example
550required size: 524288
551fully allocated size: 1074069504
552@end example
553
554The @code{required size} is the file size of the new image. It may be smaller
555than the virtual disk size if the image format supports compact representation.
556
557The @code{fully allocated size} is the file size of the new image once data has
558been written to all sectors. This is the maximum size that the image file can
559occupy with the exception of internal snapshots, dirty bitmaps, vmstate data,
560and other advanced image format features.
561
John Snow9775fcd2018-05-03 18:56:47 -0400562@item snapshot [--object @var{objectdef}] [--image-opts] [-U] [-q] [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot}] @var{filename}
blueswir1d2c639d2009-01-24 18:19:25 +0000563
564List, apply, create or delete snapshots in image @var{filename}.
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100565
John Snow9775fcd2018-05-03 18:56:47 -0400566@item rebase [--object @var{objectdef}] [--image-opts] [-U] [-q] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
Kevin Wolfe6184692011-01-17 15:35:28 +0100567
568Changes the backing file of an image. Only the formats @code{qcow2} and
569@code{qed} support changing the backing file.
570
571The backing file is changed to @var{backing_file} and (if the image format of
572@var{filename} supports this) the backing file format is changed to
Alex Bligha6166732012-10-16 13:46:18 +0100573@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty
574string), then the image is rebased onto no backing file (i.e. it will exist
575independently of any backing file).
Kevin Wolfe6184692011-01-17 15:35:28 +0100576
Fam Zhenga16efd52017-08-04 22:36:58 +0800577If a relative path name is given, the backing file is looked up relative to
578the directory containing @var{filename}.
579
Max Reitz40055952014-07-22 22:58:42 +0200580@var{cache} specifies the cache mode to be used for @var{filename}, whereas
Stefan Hajnoczi3ba67962014-09-02 11:01:03 +0100581@var{src_cache} specifies the cache mode for reading backing files.
Max Reitz40055952014-07-22 22:58:42 +0200582
Kevin Wolfe6184692011-01-17 15:35:28 +0100583There are two different modes in which @code{rebase} can operate:
584@table @option
585@item Safe mode
586This is the default mode and performs a real rebase operation. The new backing
587file may differ from the old one and qemu-img rebase will take care of keeping
588the guest-visible content of @var{filename} unchanged.
589
590In order to achieve this, any clusters that differ between @var{backing_file}
591and the old backing file of @var{filename} are merged into @var{filename}
592before actually changing the backing file.
593
594Note that the safe mode is an expensive operation, comparable to converting
595an image. It only works if the old backing file still exists.
596
597@item Unsafe mode
598qemu-img uses the unsafe mode if @code{-u} is specified. In this mode, only the
599backing file name and format of @var{filename} is changed without any checks
600on the file contents. The user must take care of specifying the correct new
601backing file, or the guest-visible content of the image will be corrupted.
602
603This mode is useful for renaming or moving the backing file to somewhere else.
604It can be used without an accessible old backing file, i.e. you can use it to
605fix an image whose backing file has already been moved/renamed.
606@end table
607
Richard W.M. Jones9fda6ab2012-05-21 14:58:05 +0100608You can use @code{rebase} to perform a ``diff'' operation on two
609disk images. This can be useful when you have copied or cloned
610a guest, and you want to get back to a thin image on top of a
611template or base image.
612
613Say that @code{base.img} has been cloned as @code{modified.img} by
614copying it, and that the @code{modified.img} guest has run so there
615are now some changes compared to @code{base.img}. To construct a thin
616image called @code{diff.qcow2} that contains just the differences, do:
617
618@example
619qemu-img create -f qcow2 -b modified.img diff.qcow2
620qemu-img rebase -b base.img diff.qcow2
621@end example
622
623At this point, @code{modified.img} can be discarded, since
624@code{base.img + diff.qcow2} contains the same information.
625
John Snow9775fcd2018-05-03 18:56:47 -0400626@item resize [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--preallocation=@var{prealloc}] [-q] [--shrink] @var{filename} [+ | -]@var{size}
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100627
628Change the disk image as if it had been created with @var{size}.
629
630Before using this command to shrink a disk image, you MUST use file system and
631partitioning tools inside the VM to reduce allocated file systems and partition
632sizes accordingly. Failure to do so will result in data loss!
633
Pavel Butsykin4ffca892017-09-18 15:42:27 +0300634When shrinking images, the @code{--shrink} option must be given. This informs
635qemu-img that the user acknowledges all loss of data beyond the truncated
636image's end.
637
Stefan Hajnocziae6b0ed2010-04-24 09:12:12 +0100638After using this command to grow a disk image, you must use file system and
639partitioning tools inside the VM to actually begin using the new space on the
640device.
Max Reitz6f176b42013-09-03 10:09:50 +0200641
Max Reitzdc5f6902017-06-13 22:20:55 +0200642When growing an image, the @code{--preallocation} option may be used to specify
643how the additional image area should be allocated on the host. See the format
644description in the @code{NOTES} section which values are allowed. Using this
645option may result in slightly more data being allocated than necessary.
646
bellardacd935e2004-11-15 22:57:26 +0000647@end table
Kevin Wolfd3067b02012-11-21 14:21:47 +0100648@c man end
bellardacd935e2004-11-15 22:57:26 +0000649
Kevin Wolfd3067b02012-11-21 14:21:47 +0100650@ignore
651@c man begin NOTES
Kevin Wolff932c042009-10-28 12:49:15 +0100652Supported image file formats:
653
654@table @option
655@item raw
656
657Raw disk image format (default). This format has the advantage of
658being simple and easily exportable to all other emulators. If your
659file system supports @emph{holes} (for example in ext2 or ext3 on
660Linux or NTFS on Windows), then only the written sectors will reserve
661space. Use @code{qemu-img info} to know the real size used by the
662image or @code{ls -ls} on Unix/Linux.
663
Hu Tao06247422014-09-10 17:05:48 +0800664Supported options:
665@table @code
666@item preallocation
667Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
668@code{falloc} mode preallocates space for image by calling posix_fallocate().
Max Reitzfa27c472019-07-11 15:29:35 +0200669@code{full} mode preallocates space for image by writing data to underlying
670storage. This data may or may not be zero, depending on the storage location.
Hu Tao06247422014-09-10 17:05:48 +0800671@end table
672
Kevin Wolff932c042009-10-28 12:49:15 +0100673@item qcow2
674QEMU image format, the most versatile format. Use it to have smaller
675images (useful if your filesystem does not supports holes, for example
676on Windows), optional AES encryption, zlib based compression and
677support of multiple VM snapshots.
Kevin Wolf8063d0f2009-10-28 12:49:16 +0100678
Kevin Wolf3e032362009-10-28 12:49:17 +0100679Supported options:
680@table @code
Kevin Wolfd3067b02012-11-21 14:21:47 +0100681@item compat
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800682Determines the qcow2 version to use. @code{compat=0.10} uses the
683traditional image format that can be read by any QEMU since 0.10.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100684@code{compat=1.1} enables image format extensions that only QEMU 1.1 and
Stefan Hajnoczi7fa9e1f2014-01-06 12:39:01 +0800685newer understand (this is the default). Amongst others, this includes zero
686clusters, which allow efficient copy-on-read for sparse images.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100687
Kevin Wolf3e032362009-10-28 12:49:17 +0100688@item backing_file
689File name of a base image (see @option{create} subcommand)
690@item backing_fmt
691Image format of the base image
692@item encryption
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000693If this option is set to @code{on}, the image is encrypted with 128-bit AES-CBC.
Kevin Wolf3e032362009-10-28 12:49:17 +0100694
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000695The use of encryption in qcow and qcow2 images is considered to be flawed by
696modern cryptography standards, suffering from a number of design problems:
697
698@itemize @minus
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100699@item
700The AES-CBC cipher is used with predictable initialization vectors based
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000701on the sector number. This makes it vulnerable to chosen plaintext attacks
702which can reveal the existence of encrypted data.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100703@item
704The user passphrase is directly used as the encryption key. A poorly
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000705chosen or short passphrase will compromise the security of the encryption.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100706@item
707In the event of the passphrase being compromised there is no way to
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000708change the passphrase to protect data in any qcow images. The files must
709be cloned, using a different encryption passphrase in the new file. The
710original file must then be securely erased using a program like shred,
711though even this is ineffective with many modern storage technologies.
Daniel P. Berrange0b4ee902017-06-23 17:24:02 +0100712@item
713Initialization vectors used to encrypt sectors are based on the
714guest virtual sector number, instead of the host physical sector. When
715a disk image has multiple internal snapshots this means that data in
716multiple physical sectors is encrypted with the same initialization
717vector. With the CBC mode, this opens the possibility of watermarking
718attacks if the attack can collect multiple sectors encrypted with the
719same IV and some predictable data. Having multiple qcow2 images with
720the same passphrase also exposes this weakness since the passphrase
721is directly used as the key.
Daniel P. Berrange136cd192014-01-22 15:47:10 +0000722@end itemize
723
724Use of qcow / qcow2 encryption is thus strongly discouraged. Users are
725recommended to use an alternative encryption technology such as the
726Linux dm-crypt / LUKS system.
Kevin Wolf3e032362009-10-28 12:49:17 +0100727
728@item cluster_size
729Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
730sizes can improve the image file size whereas larger cluster sizes generally
731provide better performance.
732
733@item preallocation
Hu Tao0e4271b2014-09-10 17:05:49 +0800734Preallocation mode (allowed values: @code{off}, @code{metadata}, @code{falloc},
735@code{full}). An image with preallocated metadata is initially larger but can
736improve performance when the image needs to grow. @code{falloc} and @code{full}
737preallocations are like the same options of @code{raw} format, but sets up
738metadata also.
Kevin Wolf3e032362009-10-28 12:49:17 +0100739
Kevin Wolfd3067b02012-11-21 14:21:47 +0100740@item lazy_refcounts
741If this option is set to @code{on}, reference count updates are postponed with
742the goal of avoiding metadata I/O and improving performance. This is
743particularly interesting with @option{cache=writethrough} which doesn't batch
744metadata updates. The tradeoff is that after a host crash, the reference count
745tables must be rebuilt, i.e. on the next open an (automatic) @code{qemu-img
746check -r all} is required, which may take some time.
747
748This option can only be enabled if @code{compat=1.1} is specified.
749
Chunyan Liu4ab15592014-06-30 14:29:58 +0800750@item nocow
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800751If this option is set to @code{on}, it will turn off COW of the file. It's only
Chunyan Liu4ab15592014-06-30 14:29:58 +0800752valid on btrfs, no effect on other file systems.
753
754Btrfs has low performance when hosting a VM image file, even more when the guest
755on the VM also using btrfs as file system. Turning off COW is a way to mitigate
756this bad performance. Generally there are two ways to turn off COW on btrfs:
757a) Disable it by mounting with nodatacow, then all newly created files will be
758NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
759does.
760
761Note: this option is only valid to new or empty files. If there is an existing
762file which is COW and has data blocks already, it couldn't be changed to NOCOW
763by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
Chunyan Liubc3a7f92014-07-02 12:27:29 +0800764the NOCOW flag is set or not (Capital 'C' is NOCOW flag).
Chunyan Liu4ab15592014-06-30 14:29:58 +0800765
Kevin Wolf3e032362009-10-28 12:49:17 +0100766@end table
767
Kevin Wolfd3067b02012-11-21 14:21:47 +0100768@item Other
769QEMU also supports various other image file formats for compatibility with
Jeff Cody8282db12013-12-17 13:56:06 -0500770older QEMU versions or other hypervisors, including VMDK, VDI, VHD (vpc), VHDX,
771qcow1 and QED. For a full list of supported formats see @code{qemu-img --help}.
Kevin Wolfd3067b02012-11-21 14:21:47 +0100772For a more detailed description of these formats, see the QEMU Emulation User
773Documentation.
Stefan Hajnoczif0858002012-06-13 14:29:15 +0100774
Kevin Wolfd3067b02012-11-21 14:21:47 +0100775The main purpose of the block drivers for these formats is image conversion.
776For running VMs, it is recommended to convert the disk images to either raw or
777qcow2 in order to achieve good performance.
Kevin Wolff932c042009-10-28 12:49:15 +0100778@end table
779
780
bellardacd935e2004-11-15 22:57:26 +0000781@c man end
782
bellardacd935e2004-11-15 22:57:26 +0000783@setfilename qemu-img
784@settitle QEMU disk image utility
785
786@c man begin SEEALSO
787The HTML documentation of QEMU for more precise information and Linux
788user mode emulator invocation.
789@c man end
790
791@c man begin AUTHOR
792Fabrice Bellard
793@c man end
794
795@end ignore